The present invention relates to a structure-borne sound sensor unit, in particular for an agricultural machine, with a signal converter, which converts a mechanical sensor signal into an electrical sensor signal, and with preprocessing electronics, which are connected with the signal converter.
The present invention also relates to a control unit for such a structure-borne sound sensor unit, a sensor system with a structure-borne sound sensor unit, and a control device of this type.
The present invention also relates to an agricultural machine with such a sensor system, and a method for controlling a structure-borne sound sensor unit of this type.
Structure-borne sound sensors, which are often referred to as “knock sensors”, are offered by various manufacturers. They are installed, in a suitable manner, on a pulse detector, e.g., directly on a suitable component of a working unit, the operating state of which is to be monitored, such that the structure-borne vibrations that occur in the particular component and that result from a certain event to be monitored can be registered by the sensor. To this end, the sensors utilize a piezo element to convert the structure-borne sound vibrations—which are usually high-frequency—into an electrical signal. Knock sensors of this type are used primarily in automotive applications. The sensors are mounted on the housing of the engine block, e.g., to regulate engine knock.
In agricultural machine technology, structure-borne sound sensors are also installed in highly diverse locations, to detect various types of vibrations and structure-borne sounds. For example, structure-borne sound sensors are used in combine harvesters to measure crop throughput and/or grain losses. To this end, a sensor of the type mentioned initially is described in EP 0 883 983 B1, which is mounted on a pulse detecting panel, which is located such that the remaining grain or waste grain in the crop material flow drops onto the pulse detecting panel and generates vibrations, which are converted into an electrical sensor signal by the signal converter. With forage harvesters, sensors of this type are used, e.g., to detect knock signals of the blades of the chopper drum on a shear bar, in order to monitor the cutting gap. An application of this type is described, e.g., in DE 30 10 416 A1. Structure-borne sound sensors can also be used in agricultural machines, e.g., as rock detectors or unbalance sensors on rotating working units.
The sensor signals must be evaluated in a control device in order to detect a certain event. With previous systems, the control device must use special input circuitry—which has been designed for the particular application of the sensor—to receive and further process the electrical signal coming from the sensor. The sensors must also be equipped differently depending on the application. There are therefore different structure-borne sound sensor units and control devices for every application. With engine knock regulation, for example, in the case of which relatively large sensor signals are produced, the sensor signals are received directly by the control device via a line connection coming from the sensor, and they are processed further in a suitable manner by the special input circuit of the control device. In the case of a knock sensor for measuring grain loss in a combine harvester, however, the measurement voltages produced at the sensor are small. Due to the losses that inevitably occur in the line from the sensor to the control device, it is therefore necessary to first amplify the signals at the sensor. The preprocessing electronics required for this are coupled directly to the sensor housing. With a sensor that is used as a loss sensor, the preprocessing electronics can also include an adjustable analog pass filter that can be adjusted for various crop materials using a preselection circuit, as described in EP 0 883 983 B1.
The disadvantage of the structure-borne sound sensor units and sensor systems described above is that they are relatively inflexible in terms of their application. Manufacturers of agricultural machines, for example, require highly diverse types of sensors and control devices with special circuitry for highly diverse applications, such as loss sensors, engine knock monitoring, unbalance sensors, cutting gap controls, etc. In terms of the manufacture of agricultural machines, this results in relatively high stockpiling costs, and it poses a problem for service, since the individual service stations must maintain stockpile a sufficient number of highly diverse sensor types and sensor control devices so they can repair a sensor system quickly when it fails. It must be taken into account that it is very costly when a machine breaks down during harvesting season, so these “down times” must be kept to a minimum.